The invention relates to a method for automatically turning off an internal-combustion engine in a vehicle, particularly in a motor vehicle having an automatic transmission, by use of a start-stop device that automatically turns off the internal-combustion engine if the vehicle is braked to a stop and is held at a stop for a predefined time interval by operating the brake pedal.
Currently, internal-combustion engines are usually turned off by the driver by use of an ignition key. A method described in DE 100 23 331 A1 represents an exception. In this case, the brake pedal position or the brake pedal pressure is analyzed instead of the ignition key. The turning-off operation of the internal-combustion engine will be initiated when, after the motor vehicle has come to a stop, the brake pedal is increasingly applied in its already applied position. Processes of this type have the disadvantage that the motor vehicle driver alone is responsible for turning-off the internal-combustion engine. Analyses of today's vehicle handling reveal that, despite an increased ecological awareness and higher fuel prices, a manual turning-off of the internal-combustion engine, for example, at traffic lights, rarely takes place independently.
In order to reduce fuel consumption and pollutant emissions, methods and systems are currently being developed, and partly also already in use, which automatically turn off the internal-combustion engine of a motor vehicle under certain conditions and automatically turn it on again under predefined turn-on conditions. Such methods and systems, or start-stop devices, are suitable mainly for city traffic for reducing fuel consumption, because, in city traffic, the vehicle often comes to a stop at traffic lights or as a result of traffic, and the operation of the internal-combustion engine will not be necessary.
A system is known, for example, from EP 0 158 605 B1, which system causes a turning-off and/or a restarting of the internal-combustion engine as a function of different conditions. One condition for initiating an automatic turning-off operation is, for example, that the vehicle speed should be below a limit value for a certain time period before the internal-combustion engine is automatically turned off.
It is a disadvantage of such methods and systems that the current traffic situation cannot be taken into account. The internal-combustion engine is therefore also turned off in those situations in which, for reasons of comfort, this is not desired by the driver. For example, an automatic turning-off of the internal-combustion engine would not be desirable in a turning lane or at a stop sign when there is the possibility of immediately continuing the drive. Particularly in the case of vehicles with an automatic transmission, provided that, during a braking operation to a stopped position, the internal-combustion engine is automatically shut off, the driver cannot prevent an automatic turning-off operation. When a reasonably priced pinion starter is used as a starting system, starter engagement, and thus a starting of the running internal-combustion engine, will not be possible or be associated with a loss of comfort since, in principle, the pinion starter is only able to engage again when the internal-combustion engine has completely shut off. This may possibly also result in longer starting times.
To prevent this problem, methods and systems are known by which the driver can prevent an automatic turning-off. EP 1 469 195 B1 discloses a method for automatically turning off an internal-combustion engine in a vehicle where, within a predefined time interval after coming to a stop, the driver can prevent the automatic turn-off operation. For example, the automatic turn-off operation will not be initiated if the driver increasingly steps on the brake pedal (applies more pressure) within the predefined time interval after coming to a stop. According to the process disclosed in EP 1 052 399 A2, an automatic engine stoppage, which in principle will be initiated when the vehicle is braked to a stop, will be prevented when the reverse gear is engaged.
It is an object of the invention to improve a method for automatically turning off an internal-combustion engine in a vehicle with and without an automatic transmission such that, when braking the vehicle to a stop, the driver can easily and intuitively prevent the automatic turn-off operation.
According to the invention, this and other objects are achieved by a method for automatically turning off an internal-combustion engine in a motor vehicle either equipped with our without an automatic transmission (including an at least partially automated transmission), by use of a start-stop device. In principle, an automatic turn-off operation will be initiated when the vehicle is braked to a stop by the driver and the stoppage is maintained for a predefined time interval. A stoppage of the vehicle will be recognized when the vehicle speed is at least almost zero or exactly zero. When the vehicle is held in its stopped position within the predefined time interval by the application of the brake pedal, the internal-combustion engine will be automatically turned off by the start-stop device. The start-stop device may, for example, be an independent control device, or may be integrated in the engine control unit.
When the driver brings the motor vehicle to a stop, for example, at a stop sign and recognizes that it is possible to immediately continue the drive, the automatic turning-off of the internal-combustion engine will not be desired. Within the predefined time interval, the driver should therefore have the opportunity to prevent the automatic turning-off operation. Accordingly, an automatic turning-off of the internal-combustion engine can be prevented by the driver when the driver releases the brake pedal within the predefined time interval after coming to a stop. In other words, the driver reduces the braking pressure applied by the brake pedal by a corresponding operation of the brake pedal. In order to be able to recognize a releasing of the brake pedal, for example, a signal of a switch, such a brake light switch, arranged in the brake pedal can be analyzed. If the brake pressure generated by the brake pedal or the brake torque is to be analyzed, the brake pressure or the torque can be determined, for example, by use of a corresponding sensor.
This method is particularly advantageous for vehicles with automatic transmissions because here, as a rule, the driver leaves the gear selector lever in the normal position when the vehicle is stopped and no clutch pedal is present which could be evaluated with respect to the driver's intention. In addition to conventional automatic transmissions, the term “automatic transmission” also applies to at least partly automated transmissions, including double clutch transmissions (transmissions with and without converters, EGS, SMG). However, this method can also be used for vehicles having manual transmissions.
The method according to the invention can further be developed such that, with the beginning of the time interval within which the automatic turning-off operation can be prevented, a holding function can be activated (in the background) for the independent holding of the vehicle when the vehicle is stopped without operating the brake. As a result, it can be ensured that the vehicle is also held in the stopped position when the driver releases the brake pedal for preventing an automatic turning-off operation.
If the holding function is not automatically activated when coming to a stop, the holding function (for preventing a rolling-away of the vehicle when the brake is released) should be automatically activated not later than when the driver releases the brake pedal for preventing the automatic turning-off operation within the time interval. If the driver does not prevent the turning-off operation, and the holding function is not yet active, in the case of a turned-off internal-combustion engine, the holding function should be activated not later than when the driver releases the brake pedal (for example, for initiating the automatic starting operation).
The term “holding function” applies to all functions or interventions which prevent at least a forward or rearward movement of the vehicle. When the driver reduces the brake pressure for releasing the brake pedal and, within the predefined time interval, prevents the automatic turning-off operation of the internal-combustion engine, the creeping function of the vehicle generated by way of a hydraulic converter can be deactivated, for example, for maintaining the stoppage of the vehicle, corresponding to an activating of the holding function. In addition or as an alternative, the vehicle can simultaneously be held in the stopped position by means of a braking intervention, which can be automatically activated in the stopped position; i.e., parking brake functions, for example, are activated for the temporary holding of an operationally ready motor vehicle in the stopped position. Such braking interventions or functions and the corresponding devices are known, for example, by the names “starting assistant”, “hill assistant”, “hill hold(er)”, “Automatic Hold” or within the scope of cruise control systems with a ranging function to the stopped position. These systems, which prevent an operationally ready motor vehicle from starting to roll, are constructed, for example, as (electro)hydraulic, (electro)pneumatic, or possibly also as electromechanical, electronically controllable braking systems, by which the operationally ready motor vehicle is temporarily held and prevented from starting to roll.
Methods are also known by which the vehicle is prevented from starting to roll by way of the transmission (particularly an automatic transmission) or by means of a corresponding transmission function. Accordingly, as an alternative or in addition to the active braking intervention or for deactivating an existing creeping function, a so-called auto-P function can be activated as a holding function for holding the vehicle in the stopped position.
In an advantageous embodiment of the method according to the invention, this automatically activated holding function for holding the vehicle in the stopped position will be deactivated when the internal-combustion engine, which was automatically switched off after the predefined time interval after the vehicle had come to a stop, is automatically switched on, and/or when the gas pedal is operated and/or when the internal-combustion engine provides a sufficiently large drive torque for accelerating the vehicle from the stopped position.
If the driver does not release the brake pedal within the predefined time interval after the vehicle has come to a stop, the internal-combustion engine will be automatically turned off after the expiration of the time interval. Simultaneously, the turning-off of the internal-combustion engine can also activate a holding function. If the holding function had already been activated, it may remain active.
Advantageously, the automatically turned-off internal-combustion engine will automatically be turned on again: (1) when the driver releases the brake pedal, (2) when the brake pressure applied by the driver falls below a predefined brake pressure threshold value, (3) when the brake torque applied by the driver falls below a predefined brake torque threshold value, and/or (4) when the negative braking gradient (brake torque gradient or brake pressure gradient) reached when the brake pedal is released, reaches or exceeds a predefined braking gradient threshold value or when the driver operates the gas pedal.
In order to prevent the vehicle from rolling away even before the start of the internal-combustion engine—as illustrated above—while the internal-combustion engine is turned off, a holding function or a parking brake function, particularly an auto hold function can be activated not later than simultaneously with the release of the brake pedal or with the reduction of the brake pressure applied by the driver. This auto-hold function remains active until the drive unit is started, and the vehicle starts to move or could start to move either as a result of the gas pedal operation or of the creeping function.
Advantageously, the motor vehicle driver can be informed by way of a first indicating element as soon as he can prevent the automatic turning-off of the internal-combustion engine. When the predefined operating conditions have been met, i.e. the vehicle was braked to a stop and all other conditions were also met, for example, an LED will light up signaling to the driver that the internal-combustion engine will shortly be turned off by the start-stop device. However, loudspeakers for an acoustic signal or other elements for visual or haptic signals may also be used as indicating elements. Starting at this point-in-time, the motor vehicle driver can prevent the turning-off of the internal-combustion engine. As an alternative or in addition, a second indicating element can be activated if the internal-combustion engine was automatically turned off. The second indicating element may be further developed such that it informs the driver as to how or by which action he can again initiate a start of the internal-combustion engine. If this can take place, for example, by releasing the brake pedal, a brake pedal symbol will be displayed from which the foot is moving away.
As an alternative or in addition, a third indicating element can be activated for the duration of the active holding function, so that the driver knows that the vehicle is maintained in the stopped position despite the releasing of the brake pedal.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.